1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
//! BigNum implementation
//!
//! Large numbers are important for a cryptographic library.  OpenSSL implementation
//! of BigNum uses dynamically assigned memory to store an array of bit chunks.  This
//! allows numbers of any size to be compared and mathematical functions performed.
//!
//! OpenSSL wiki describes the [`BIGNUM`] data structure.
//!
//! # Examples
//!
//! ```
//! use openssl::bn::BigNum;
//! use openssl::error::ErrorStack;
//!
//! fn main() -> Result<(), ErrorStack> {
//!   let a = BigNum::new()?; // a = 0
//!   let b = BigNum::from_dec_str("1234567890123456789012345")?;
//!   let c = &a * &b;
//!   assert_eq!(a, c);
//!   Ok(())
//! }
//! ```
//!
//! [`BIGNUM`]: https://wiki.openssl.org/index.php/Manual:Bn_internal(3)
use cfg_if::cfg_if;
use foreign_types::{ForeignType, ForeignTypeRef};
use libc::c_int;
use std::cmp::Ordering;
use std::ffi::CString;
use std::ops::{Add, Deref, Div, Mul, Neg, Rem, Shl, Shr, Sub};
use std::{fmt, ptr};

use crate::asn1::Asn1Integer;
use crate::error::ErrorStack;
use crate::string::OpensslString;
use crate::{cvt, cvt_n, cvt_p, LenType};
use openssl_macros::corresponds;

cfg_if! {
    if #[cfg(any(ossl110, libressl350))] {
        use ffi::{
            BN_get_rfc2409_prime_1024, BN_get_rfc2409_prime_768, BN_get_rfc3526_prime_1536,
            BN_get_rfc3526_prime_2048, BN_get_rfc3526_prime_3072, BN_get_rfc3526_prime_4096,
            BN_get_rfc3526_prime_6144, BN_get_rfc3526_prime_8192, BN_is_negative,
        };
    } else if #[cfg(boringssl)] {
        use ffi::BN_is_negative;
    } else {
        use ffi::{
            get_rfc2409_prime_1024 as BN_get_rfc2409_prime_1024,
            get_rfc2409_prime_768 as BN_get_rfc2409_prime_768,
            get_rfc3526_prime_1536 as BN_get_rfc3526_prime_1536,
            get_rfc3526_prime_2048 as BN_get_rfc3526_prime_2048,
            get_rfc3526_prime_3072 as BN_get_rfc3526_prime_3072,
            get_rfc3526_prime_4096 as BN_get_rfc3526_prime_4096,
            get_rfc3526_prime_6144 as BN_get_rfc3526_prime_6144,
            get_rfc3526_prime_8192 as BN_get_rfc3526_prime_8192,
        };

        #[allow(bad_style)]
        unsafe fn BN_is_negative(bn: *const ffi::BIGNUM) -> c_int {
            (*bn).neg
        }
    }
}

/// Options for the most significant bits of a randomly generated `BigNum`.
pub struct MsbOption(c_int);

impl MsbOption {
    /// The most significant bit of the number may be 0.
    pub const MAYBE_ZERO: MsbOption = MsbOption(-1);

    /// The most significant bit of the number must be 1.
    pub const ONE: MsbOption = MsbOption(0);

    /// The most significant two bits of the number must be 1.
    ///
    /// The number of bits in the product of two such numbers will always be exactly twice the
    /// number of bits in the original numbers.
    pub const TWO_ONES: MsbOption = MsbOption(1);
}

foreign_type_and_impl_send_sync! {
    type CType = ffi::BN_CTX;
    fn drop = ffi::BN_CTX_free;

    /// Temporary storage for BigNums on the secure heap
    ///
    /// BigNum values are stored dynamically and therefore can be expensive
    /// to allocate.  BigNumContext and the OpenSSL [`BN_CTX`] structure are used
    /// internally when passing BigNum values between subroutines.
    ///
    /// [`BN_CTX`]: https://www.openssl.org/docs/manmaster/crypto/BN_CTX_new.html
    pub struct BigNumContext;
    /// Reference to [`BigNumContext`]
    ///
    /// [`BigNumContext`]: struct.BigNumContext.html
    pub struct BigNumContextRef;
}

impl BigNumContext {
    /// Returns a new `BigNumContext`.
    #[corresponds(BN_CTX_new)]
    pub fn new() -> Result<BigNumContext, ErrorStack> {
        unsafe {
            ffi::init();
            cvt_p(ffi::BN_CTX_new()).map(BigNumContext)
        }
    }

    /// Returns a new secure `BigNumContext`.
    #[corresponds(BN_CTX_secure_new)]
    #[cfg(ossl110)]
    pub fn new_secure() -> Result<BigNumContext, ErrorStack> {
        unsafe {
            ffi::init();
            cvt_p(ffi::BN_CTX_secure_new()).map(BigNumContext)
        }
    }
}

foreign_type_and_impl_send_sync! {
    type CType = ffi::BIGNUM;
    fn drop = ffi::BN_free;

    /// Dynamically sized large number implementation
    ///
    /// Perform large number mathematics.  Create a new BigNum
    /// with [`new`].  Perform standard mathematics on large numbers using
    /// methods from [`Dref<Target = BigNumRef>`]
    ///
    /// OpenSSL documentation at [`BN_new`].
    ///
    /// [`new`]: struct.BigNum.html#method.new
    /// [`Dref<Target = BigNumRef>`]: struct.BigNum.html#deref-methods
    /// [`BN_new`]: https://www.openssl.org/docs/manmaster/crypto/BN_new.html
    ///
    /// # Examples
    /// ```
    /// use openssl::bn::BigNum;
    /// # use openssl::error::ErrorStack;
    /// # fn bignums() -> Result< (), ErrorStack > {
    /// let little_big = BigNum::from_u32(std::u32::MAX)?;
    /// assert_eq!(*&little_big.num_bytes(), 4);
    /// # Ok(())
    /// # }
    /// # fn main () { bignums(); }
    /// ```
    pub struct BigNum;
    /// Reference to a [`BigNum`]
    ///
    /// [`BigNum`]: struct.BigNum.html
    pub struct BigNumRef;
}

impl BigNumRef {
    /// Erases the memory used by this `BigNum`, resetting its value to 0.
    ///
    /// This can be used to destroy sensitive data such as keys when they are no longer needed.
    #[corresponds(BN_clear)]
    pub fn clear(&mut self) {
        unsafe { ffi::BN_clear(self.as_ptr()) }
    }

    /// Adds a `u32` to `self`.
    #[corresponds(BN_add_word)]
    pub fn add_word(&mut self, w: u32) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_add_word(self.as_ptr(), w as ffi::BN_ULONG)).map(|_| ()) }
    }

    /// Subtracts a `u32` from `self`.
    #[corresponds(BN_sub_word)]
    pub fn sub_word(&mut self, w: u32) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_sub_word(self.as_ptr(), w as ffi::BN_ULONG)).map(|_| ()) }
    }

    /// Multiplies a `u32` by `self`.
    #[corresponds(BN_mul_word)]
    pub fn mul_word(&mut self, w: u32) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_mul_word(self.as_ptr(), w as ffi::BN_ULONG)).map(|_| ()) }
    }

    /// Divides `self` by a `u32`, returning the remainder.
    #[corresponds(BN_div_word)]
    #[allow(clippy::useless_conversion)]
    pub fn div_word(&mut self, w: u32) -> Result<u64, ErrorStack> {
        unsafe {
            let r = ffi::BN_div_word(self.as_ptr(), w.into());
            if r == ffi::BN_ULONG::MAX {
                Err(ErrorStack::get())
            } else {
                Ok(r.into())
            }
        }
    }

    /// Returns the result of `self` modulo `w`.
    #[corresponds(BN_mod_word)]
    #[allow(clippy::useless_conversion)]
    pub fn mod_word(&self, w: u32) -> Result<u64, ErrorStack> {
        unsafe {
            let r = ffi::BN_mod_word(self.as_ptr(), w.into());
            if r == ffi::BN_ULONG::MAX {
                Err(ErrorStack::get())
            } else {
                Ok(r.into())
            }
        }
    }

    /// Places a cryptographically-secure pseudo-random nonnegative
    /// number less than `self` in `rnd`.
    #[corresponds(BN_rand_range)]
    pub fn rand_range(&self, rnd: &mut BigNumRef) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_rand_range(rnd.as_ptr(), self.as_ptr())).map(|_| ()) }
    }

    /// The cryptographically weak counterpart to `rand_in_range`.
    #[cfg(not(osslconf = "OPENSSL_NO_DEPRECATED_3_0"))]
    #[corresponds(BN_pseudo_rand_range)]
    pub fn pseudo_rand_range(&self, rnd: &mut BigNumRef) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_pseudo_rand_range(rnd.as_ptr(), self.as_ptr())).map(|_| ()) }
    }

    /// Sets bit `n`. Equivalent to `self |= (1 << n)`.
    ///
    /// When setting a bit outside of `self`, it is expanded.
    #[corresponds(BN_set_bit)]
    #[allow(clippy::useless_conversion)]
    pub fn set_bit(&mut self, n: i32) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_set_bit(self.as_ptr(), n.into())).map(|_| ()) }
    }

    /// Clears bit `n`, setting it to 0. Equivalent to `self &= ~(1 << n)`.
    ///
    /// When clearing a bit outside of `self`, an error is returned.
    #[corresponds(BN_clear_bit)]
    #[allow(clippy::useless_conversion)]
    pub fn clear_bit(&mut self, n: i32) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_clear_bit(self.as_ptr(), n.into())).map(|_| ()) }
    }

    /// Returns `true` if the `n`th bit of `self` is set to 1, `false` otherwise.
    #[corresponds(BN_is_bit_set)]
    #[allow(clippy::useless_conversion)]
    pub fn is_bit_set(&self, n: i32) -> bool {
        unsafe { ffi::BN_is_bit_set(self.as_ptr(), n.into()) == 1 }
    }

    /// Truncates `self` to the lowest `n` bits.
    ///
    /// An error occurs if `self` is already shorter than `n` bits.
    #[corresponds(BN_mask_bits)]
    #[allow(clippy::useless_conversion)]
    pub fn mask_bits(&mut self, n: i32) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_mask_bits(self.as_ptr(), n.into())).map(|_| ()) }
    }

    /// Places `a << 1` in `self`.  Equivalent to `self * 2`.
    #[corresponds(BN_lshift1)]
    pub fn lshift1(&mut self, a: &BigNumRef) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_lshift1(self.as_ptr(), a.as_ptr())).map(|_| ()) }
    }

    /// Places `a >> 1` in `self`. Equivalent to `self / 2`.
    #[corresponds(BN_rshift1)]
    pub fn rshift1(&mut self, a: &BigNumRef) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_rshift1(self.as_ptr(), a.as_ptr())).map(|_| ()) }
    }

    /// Places `a + b` in `self`.  [`core::ops::Add`] is also implemented for `BigNumRef`.
    ///
    /// [`core::ops::Add`]: struct.BigNumRef.html#method.add
    #[corresponds(BN_add)]
    pub fn checked_add(&mut self, a: &BigNumRef, b: &BigNumRef) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_add(self.as_ptr(), a.as_ptr(), b.as_ptr())).map(|_| ()) }
    }

    /// Places `a - b` in `self`. [`core::ops::Sub`] is also implemented for `BigNumRef`.
    ///
    /// [`core::ops::Sub`]: struct.BigNumRef.html#method.sub
    #[corresponds(BN_sub)]
    pub fn checked_sub(&mut self, a: &BigNumRef, b: &BigNumRef) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_sub(self.as_ptr(), a.as_ptr(), b.as_ptr())).map(|_| ()) }
    }

    /// Places `a << n` in `self`.  Equivalent to `a * 2 ^ n`.
    #[corresponds(BN_lshift)]
    #[allow(clippy::useless_conversion)]
    pub fn lshift(&mut self, a: &BigNumRef, n: i32) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_lshift(self.as_ptr(), a.as_ptr(), n.into())).map(|_| ()) }
    }

    /// Places `a >> n` in `self`. Equivalent to `a / 2 ^ n`.
    #[corresponds(BN_rshift)]
    #[allow(clippy::useless_conversion)]
    pub fn rshift(&mut self, a: &BigNumRef, n: i32) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_rshift(self.as_ptr(), a.as_ptr(), n.into())).map(|_| ()) }
    }

    /// Creates a new BigNum with the same value.
    #[corresponds(BN_dup)]
    pub fn to_owned(&self) -> Result<BigNum, ErrorStack> {
        unsafe { cvt_p(ffi::BN_dup(self.as_ptr())).map(|b| BigNum::from_ptr(b)) }
    }

    /// Sets the sign of `self`.  Pass true to set `self` to a negative.  False sets
    /// `self` positive.
    #[corresponds(BN_set_negative)]
    pub fn set_negative(&mut self, negative: bool) {
        unsafe { ffi::BN_set_negative(self.as_ptr(), negative as c_int) }
    }

    /// Compare the absolute values of `self` and `oth`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use openssl::bn::BigNum;
    /// # use std::cmp::Ordering;
    /// let s = -BigNum::from_u32(8).unwrap();
    /// let o = BigNum::from_u32(8).unwrap();
    ///
    /// assert_eq!(s.ucmp(&o), Ordering::Equal);
    /// ```
    #[corresponds(BN_ucmp)]
    pub fn ucmp(&self, oth: &BigNumRef) -> Ordering {
        unsafe { ffi::BN_ucmp(self.as_ptr(), oth.as_ptr()).cmp(&0) }
    }

    /// Returns `true` if `self` is negative.
    #[corresponds(BN_is_negative)]
    pub fn is_negative(&self) -> bool {
        unsafe { BN_is_negative(self.as_ptr()) == 1 }
    }

    /// Returns `true` is `self` is even.
    #[corresponds(BN_is_even)]
    #[cfg(any(ossl110, boringssl, libressl350))]
    pub fn is_even(&self) -> bool {
        !self.is_odd()
    }

    /// Returns `true` is `self` is odd.
    #[corresponds(BN_is_odd)]
    #[cfg(any(ossl110, boringssl, libressl350))]
    pub fn is_odd(&self) -> bool {
        unsafe { ffi::BN_is_odd(self.as_ptr()) == 1 }
    }

    /// Returns the number of significant bits in `self`.
    #[corresponds(BN_num_bits)]
    #[allow(clippy::unnecessary_cast)]
    pub fn num_bits(&self) -> i32 {
        unsafe { ffi::BN_num_bits(self.as_ptr()) as i32 }
    }

    /// Returns the size of `self` in bytes. Implemented natively.
    pub fn num_bytes(&self) -> i32 {
        (self.num_bits() + 7) / 8
    }

    /// Generates a cryptographically strong pseudo-random `BigNum`, placing it in `self`.
    ///
    /// # Parameters
    ///
    /// * `bits`: Length of the number in bits.
    /// * `msb`: The desired properties of the most significant bit. See [`constants`].
    /// * `odd`: If `true`, the generated number will be odd.
    ///
    /// # Examples
    ///
    /// ```
    /// use openssl::bn::{BigNum, MsbOption};
    /// use openssl::error::ErrorStack;
    ///
    /// fn generate_random() -> Result< BigNum, ErrorStack > {
    ///    let mut big = BigNum::new()?;
    ///
    ///    // Generates a 128-bit odd random number
    ///    big.rand(128, MsbOption::MAYBE_ZERO, true);
    ///    Ok((big))
    /// }
    /// ```
    ///
    /// [`constants`]: index.html#constants
    #[corresponds(BN_rand)]
    #[allow(clippy::useless_conversion)]
    pub fn rand(&mut self, bits: i32, msb: MsbOption, odd: bool) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_rand(
                self.as_ptr(),
                bits.into(),
                msb.0,
                odd as c_int,
            ))
            .map(|_| ())
        }
    }

    /// The cryptographically weak counterpart to `rand`.  Not suitable for key generation.
    #[cfg(not(osslconf = "OPENSSL_NO_DEPRECATED_3_0"))]
    #[corresponds(BN_pseudo_rand)]
    #[allow(clippy::useless_conversion)]
    pub fn pseudo_rand(&mut self, bits: i32, msb: MsbOption, odd: bool) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_pseudo_rand(
                self.as_ptr(),
                bits.into(),
                msb.0,
                odd as c_int,
            ))
            .map(|_| ())
        }
    }

    /// Generates a prime number, placing it in `self`.
    ///
    /// # Parameters
    ///
    /// * `bits`: The length of the prime in bits (lower bound).
    /// * `safe`: If true, returns a "safe" prime `p` so that `(p-1)/2` is also prime.
    /// * `add`/`rem`: If `add` is set to `Some(add)`, `p % add == rem` will hold, where `p` is the
    ///   generated prime and `rem` is `1` if not specified (`None`).
    ///
    /// # Examples
    ///
    /// ```
    /// use openssl::bn::BigNum;
    /// use openssl::error::ErrorStack;
    ///
    /// fn generate_weak_prime() -> Result< BigNum, ErrorStack > {
    ///    let mut big = BigNum::new()?;
    ///
    ///    // Generates a 128-bit simple prime number
    ///    big.generate_prime(128, false, None, None);
    ///    Ok((big))
    /// }
    /// ```
    #[corresponds(BN_generate_prime_ex)]
    pub fn generate_prime(
        &mut self,
        bits: i32,
        safe: bool,
        add: Option<&BigNumRef>,
        rem: Option<&BigNumRef>,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_generate_prime_ex(
                self.as_ptr(),
                bits as c_int,
                safe as c_int,
                add.map(|n| n.as_ptr()).unwrap_or(ptr::null_mut()),
                rem.map(|n| n.as_ptr()).unwrap_or(ptr::null_mut()),
                ptr::null_mut(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `a * b` in `self`.
    /// [`core::ops::Mul`] is also implemented for `BigNumRef`.
    ///
    /// [`core::ops::Mul`]: struct.BigNumRef.html#method.mul
    #[corresponds(BN_mul)]
    pub fn checked_mul(
        &mut self,
        a: &BigNumRef,
        b: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_mul(
                self.as_ptr(),
                a.as_ptr(),
                b.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `a / b` in `self`. The remainder is discarded.
    /// [`core::ops::Div`] is also implemented for `BigNumRef`.
    ///
    /// [`core::ops::Div`]: struct.BigNumRef.html#method.div
    #[corresponds(BN_div)]
    pub fn checked_div(
        &mut self,
        a: &BigNumRef,
        b: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_div(
                self.as_ptr(),
                ptr::null_mut(),
                a.as_ptr(),
                b.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `a % b` in `self`.
    #[corresponds(BN_div)]
    pub fn checked_rem(
        &mut self,
        a: &BigNumRef,
        b: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_div(
                ptr::null_mut(),
                self.as_ptr(),
                a.as_ptr(),
                b.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `a / b` in `self` and `a % b` in `rem`.
    #[corresponds(BN_div)]
    pub fn div_rem(
        &mut self,
        rem: &mut BigNumRef,
        a: &BigNumRef,
        b: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_div(
                self.as_ptr(),
                rem.as_ptr(),
                a.as_ptr(),
                b.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `a²` in `self`.
    #[corresponds(BN_sqr)]
    pub fn sqr(&mut self, a: &BigNumRef, ctx: &mut BigNumContextRef) -> Result<(), ErrorStack> {
        unsafe { cvt(ffi::BN_sqr(self.as_ptr(), a.as_ptr(), ctx.as_ptr())).map(|_| ()) }
    }

    /// Places the result of `a mod m` in `self`.  As opposed to `div_rem`
    /// the result is non-negative.
    #[corresponds(BN_nnmod)]
    pub fn nnmod(
        &mut self,
        a: &BigNumRef,
        m: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_nnmod(
                self.as_ptr(),
                a.as_ptr(),
                m.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `(a + b) mod m` in `self`.
    #[corresponds(BN_mod_add)]
    pub fn mod_add(
        &mut self,
        a: &BigNumRef,
        b: &BigNumRef,
        m: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_mod_add(
                self.as_ptr(),
                a.as_ptr(),
                b.as_ptr(),
                m.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `(a - b) mod m` in `self`.
    #[corresponds(BN_mod_sub)]
    pub fn mod_sub(
        &mut self,
        a: &BigNumRef,
        b: &BigNumRef,
        m: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_mod_sub(
                self.as_ptr(),
                a.as_ptr(),
                b.as_ptr(),
                m.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `(a * b) mod m` in `self`.
    #[corresponds(BN_mod_mul)]
    pub fn mod_mul(
        &mut self,
        a: &BigNumRef,
        b: &BigNumRef,
        m: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_mod_mul(
                self.as_ptr(),
                a.as_ptr(),
                b.as_ptr(),
                m.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `a² mod m` in `self`.
    #[corresponds(BN_mod_sqr)]
    pub fn mod_sqr(
        &mut self,
        a: &BigNumRef,
        m: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_mod_sqr(
                self.as_ptr(),
                a.as_ptr(),
                m.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places into `self` the modular square root of `a` such that `self^2 = a (mod p)`
    #[corresponds(BN_mod_sqrt)]
    pub fn mod_sqrt(
        &mut self,
        a: &BigNumRef,
        p: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt_p(ffi::BN_mod_sqrt(
                self.as_ptr(),
                a.as_ptr(),
                p.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `a^p` in `self`.
    #[corresponds(BN_exp)]
    pub fn exp(
        &mut self,
        a: &BigNumRef,
        p: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_exp(
                self.as_ptr(),
                a.as_ptr(),
                p.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the result of `a^p mod m` in `self`.
    #[corresponds(BN_mod_exp)]
    pub fn mod_exp(
        &mut self,
        a: &BigNumRef,
        p: &BigNumRef,
        m: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_mod_exp(
                self.as_ptr(),
                a.as_ptr(),
                p.as_ptr(),
                m.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the inverse of `a` modulo `n` in `self`.
    #[corresponds(BN_mod_inverse)]
    pub fn mod_inverse(
        &mut self,
        a: &BigNumRef,
        n: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt_p(ffi::BN_mod_inverse(
                self.as_ptr(),
                a.as_ptr(),
                n.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Places the greatest common denominator of `a` and `b` in `self`.
    #[corresponds(BN_gcd)]
    pub fn gcd(
        &mut self,
        a: &BigNumRef,
        b: &BigNumRef,
        ctx: &mut BigNumContextRef,
    ) -> Result<(), ErrorStack> {
        unsafe {
            cvt(ffi::BN_gcd(
                self.as_ptr(),
                a.as_ptr(),
                b.as_ptr(),
                ctx.as_ptr(),
            ))
            .map(|_| ())
        }
    }

    /// Checks whether `self` is prime.
    ///
    /// Performs a Miller-Rabin probabilistic primality test with `checks` iterations.
    ///
    /// # Return Value
    ///
    /// Returns `true` if `self` is prime with an error probability of less than `0.25 ^ checks`.
    #[cfg(not(osslconf = "OPENSSL_NO_DEPRECATED_3_0"))]
    #[corresponds(BN_is_prime_ex)]
    #[allow(clippy::useless_conversion)]
    pub fn is_prime(&self, checks: i32, ctx: &mut BigNumContextRef) -> Result<bool, ErrorStack> {
        unsafe {
            cvt_n(ffi::BN_is_prime_ex(
                self.as_ptr(),
                checks.into(),
                ctx.as_ptr(),
                ptr::null_mut(),
            ))
            .map(|r| r != 0)
        }
    }

    /// Checks whether `self` is prime with optional trial division.
    ///
    /// If `do_trial_division` is `true`, first performs trial division by a number of small primes.
    /// Then, like `is_prime`, performs a Miller-Rabin probabilistic primality test with `checks`
    /// iterations.
    ///
    /// # Return Value
    ///
    /// Returns `true` if `self` is prime with an error probability of less than `0.25 ^ checks`.
    #[cfg(not(osslconf = "OPENSSL_NO_DEPRECATED_3_0"))]
    #[corresponds(BN_is_prime_fasttest_ex)]
    #[allow(clippy::useless_conversion)]
    pub fn is_prime_fasttest(
        &self,
        checks: i32,
        ctx: &mut BigNumContextRef,
        do_trial_division: bool,
    ) -> Result<bool, ErrorStack> {
        unsafe {
            cvt_n(ffi::BN_is_prime_fasttest_ex(
                self.as_ptr(),
                checks.into(),
                ctx.as_ptr(),
                do_trial_division as c_int,
                ptr::null_mut(),
            ))
            .map(|r| r != 0)
        }
    }

    /// Returns a big-endian byte vector representation of the absolute value of `self`.
    ///
    /// `self` can be recreated by using `from_slice`.
    ///
    /// ```
    /// # use openssl::bn::BigNum;
    /// let s = -BigNum::from_u32(4543).unwrap();
    /// let r = BigNum::from_u32(4543).unwrap();
    ///
    /// let s_vec = s.to_vec();
    /// assert_eq!(BigNum::from_slice(&s_vec).unwrap(), r);
    /// ```
    #[corresponds(BN_bn2bin)]
    pub fn to_vec(&self) -> Vec<u8> {
        let size = self.num_bytes() as usize;
        let mut v = Vec::with_capacity(size);
        unsafe {
            ffi::BN_bn2bin(self.as_ptr(), v.as_mut_ptr());
            v.set_len(size);
        }
        v
    }

    /// Returns a big-endian byte vector representation of the absolute value of `self` padded
    /// to `pad_to` bytes.
    ///
    /// If `pad_to` is less than `self.num_bytes()` then an error is returned.
    ///
    /// `self` can be recreated by using `from_slice`.
    ///
    /// ```
    /// # use openssl::bn::BigNum;
    /// let bn = BigNum::from_u32(0x4543).unwrap();
    ///
    /// let bn_vec = bn.to_vec_padded(4).unwrap();
    /// assert_eq!(&bn_vec, &[0, 0, 0x45, 0x43]);
    ///
    /// let r = bn.to_vec_padded(1);
    /// assert!(r.is_err());
    ///
    /// let bn = -BigNum::from_u32(0x4543).unwrap();
    /// let bn_vec = bn.to_vec_padded(4).unwrap();
    /// assert_eq!(&bn_vec, &[0, 0, 0x45, 0x43]);
    /// ```
    #[corresponds(BN_bn2binpad)]
    #[cfg(any(ossl110, libressl340, boringssl))]
    pub fn to_vec_padded(&self, pad_to: i32) -> Result<Vec<u8>, ErrorStack> {
        let mut v = Vec::with_capacity(pad_to as usize);
        unsafe {
            cvt(ffi::BN_bn2binpad(self.as_ptr(), v.as_mut_ptr(), pad_to))?;
            v.set_len(pad_to as usize);
        }
        Ok(v)
    }

    /// Returns a decimal string representation of `self`.
    ///
    /// ```
    /// # use openssl::bn::BigNum;
    /// let s = -BigNum::from_u32(12345).unwrap();
    ///
    /// assert_eq!(&**s.to_dec_str().unwrap(), "-12345");
    /// ```
    #[corresponds(BN_bn2dec)]
    pub fn to_dec_str(&self) -> Result<OpensslString, ErrorStack> {
        unsafe {
            let buf = cvt_p(ffi::BN_bn2dec(self.as_ptr()))?;
            Ok(OpensslString::from_ptr(buf))
        }
    }

    /// Returns a hexadecimal string representation of `self`.
    ///
    /// ```
    /// # use openssl::bn::BigNum;
    /// let s = -BigNum::from_u32(0x99ff).unwrap();
    ///
    /// assert_eq!(s.to_hex_str().unwrap().to_uppercase(), "-99FF");
    /// ```
    #[corresponds(BN_bn2hex)]
    pub fn to_hex_str(&self) -> Result<OpensslString, ErrorStack> {
        unsafe {
            let buf = cvt_p(ffi::BN_bn2hex(self.as_ptr()))?;
            Ok(OpensslString::from_ptr(buf))
        }
    }

    /// Returns an `Asn1Integer` containing the value of `self`.
    #[corresponds(BN_to_ASN1_INTEGER)]
    pub fn to_asn1_integer(&self) -> Result<Asn1Integer, ErrorStack> {
        unsafe {
            cvt_p(ffi::BN_to_ASN1_INTEGER(self.as_ptr(), ptr::null_mut()))
                .map(|p| Asn1Integer::from_ptr(p))
        }
    }

    /// Force constant time computation on this value.
    #[corresponds(BN_set_flags)]
    #[cfg(ossl110)]
    pub fn set_const_time(&mut self) {
        unsafe { ffi::BN_set_flags(self.as_ptr(), ffi::BN_FLG_CONSTTIME) }
    }

    /// Returns true if `self` is in const time mode.
    #[corresponds(BN_get_flags)]
    #[cfg(ossl110)]
    pub fn is_const_time(&self) -> bool {
        unsafe {
            let ret = ffi::BN_get_flags(self.as_ptr(), ffi::BN_FLG_CONSTTIME);
            ret == ffi::BN_FLG_CONSTTIME
        }
    }

    /// Returns true if `self` was created with [`BigNum::new_secure`].
    #[corresponds(BN_get_flags)]
    #[cfg(ossl110)]
    pub fn is_secure(&self) -> bool {
        unsafe {
            let ret = ffi::BN_get_flags(self.as_ptr(), ffi::BN_FLG_SECURE);
            ret == ffi::BN_FLG_SECURE
        }
    }
}

impl BigNum {
    /// Creates a new `BigNum` with the value 0.
    #[corresponds(BN_new)]
    pub fn new() -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            let v = cvt_p(ffi::BN_new())?;
            Ok(BigNum::from_ptr(v))
        }
    }

    /// Returns a new secure `BigNum`.
    #[corresponds(BN_secure_new)]
    #[cfg(ossl110)]
    pub fn new_secure() -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            let v = cvt_p(ffi::BN_secure_new())?;
            Ok(BigNum::from_ptr(v))
        }
    }

    /// Creates a new `BigNum` with the given value.
    #[corresponds(BN_set_word)]
    pub fn from_u32(n: u32) -> Result<BigNum, ErrorStack> {
        BigNum::new().and_then(|v| unsafe {
            cvt(ffi::BN_set_word(v.as_ptr(), n as ffi::BN_ULONG)).map(|_| v)
        })
    }

    /// Creates a `BigNum` from a decimal string.
    #[corresponds(BN_dec2bn)]
    pub fn from_dec_str(s: &str) -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            let c_str = CString::new(s.as_bytes()).unwrap();
            let mut bn = ptr::null_mut();
            cvt(ffi::BN_dec2bn(&mut bn, c_str.as_ptr() as *const _))?;
            Ok(BigNum::from_ptr(bn))
        }
    }

    /// Creates a `BigNum` from a hexadecimal string.
    #[corresponds(BN_hex2bn)]
    pub fn from_hex_str(s: &str) -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            let c_str = CString::new(s.as_bytes()).unwrap();
            let mut bn = ptr::null_mut();
            cvt(ffi::BN_hex2bn(&mut bn, c_str.as_ptr() as *const _))?;
            Ok(BigNum::from_ptr(bn))
        }
    }

    /// Returns a constant used in IKE as defined in [`RFC 2409`].  This prime number is in
    /// the order of magnitude of `2 ^ 768`.  This number is used during calculated key
    /// exchanges such as Diffie-Hellman.  This number is labeled Oakley group id 1.
    ///
    /// [`RFC 2409`]: https://tools.ietf.org/html/rfc2409#page-21
    #[corresponds(BN_get_rfc2409_prime_768)]
    #[cfg(not(boringssl))]
    pub fn get_rfc2409_prime_768() -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            cvt_p(BN_get_rfc2409_prime_768(ptr::null_mut())).map(BigNum)
        }
    }

    /// Returns a constant used in IKE as defined in [`RFC 2409`].  This prime number is in
    /// the order of magnitude of `2 ^ 1024`.  This number is used during calculated key
    /// exchanges such as Diffie-Hellman.  This number is labeled Oakly group 2.
    ///
    /// [`RFC 2409`]: https://tools.ietf.org/html/rfc2409#page-21
    #[corresponds(BN_get_rfc2409_prime_1024)]
    #[cfg(not(boringssl))]
    pub fn get_rfc2409_prime_1024() -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            cvt_p(BN_get_rfc2409_prime_1024(ptr::null_mut())).map(BigNum)
        }
    }

    /// Returns a constant used in IKE as defined in [`RFC 3526`].  The prime is in the order
    /// of magnitude of `2 ^ 1536`.  This number is used during calculated key
    /// exchanges such as Diffie-Hellman.  This number is labeled MODP group 5.
    ///
    /// [`RFC 3526`]: https://tools.ietf.org/html/rfc3526#page-3
    #[corresponds(BN_get_rfc3526_prime_1536)]
    #[cfg(not(boringssl))]
    pub fn get_rfc3526_prime_1536() -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            cvt_p(BN_get_rfc3526_prime_1536(ptr::null_mut())).map(BigNum)
        }
    }

    /// Returns a constant used in IKE as defined in [`RFC 3526`].  The prime is in the order
    /// of magnitude of `2 ^ 2048`.  This number is used during calculated key
    /// exchanges such as Diffie-Hellman.  This number is labeled MODP group 14.
    ///
    /// [`RFC 3526`]: https://tools.ietf.org/html/rfc3526#page-3
    #[corresponds(BN_get_rfc3526_prime_2048)]
    #[cfg(not(boringssl))]
    pub fn get_rfc3526_prime_2048() -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            cvt_p(BN_get_rfc3526_prime_2048(ptr::null_mut())).map(BigNum)
        }
    }

    /// Returns a constant used in IKE as defined in [`RFC 3526`].  The prime is in the order
    /// of magnitude of `2 ^ 3072`.  This number is used during calculated key
    /// exchanges such as Diffie-Hellman.  This number is labeled MODP group 15.
    ///
    /// [`RFC 3526`]: https://tools.ietf.org/html/rfc3526#page-4
    #[corresponds(BN_get_rfc3526_prime_3072)]
    #[cfg(not(boringssl))]
    pub fn get_rfc3526_prime_3072() -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            cvt_p(BN_get_rfc3526_prime_3072(ptr::null_mut())).map(BigNum)
        }
    }

    /// Returns a constant used in IKE as defined in [`RFC 3526`].  The prime is in the order
    /// of magnitude of `2 ^ 4096`.  This number is used during calculated key
    /// exchanges such as Diffie-Hellman.  This number is labeled MODP group 16.
    ///
    /// [`RFC 3526`]: https://tools.ietf.org/html/rfc3526#page-4
    #[corresponds(BN_get_rfc3526_prime_4096)]
    #[cfg(not(boringssl))]
    pub fn get_rfc3526_prime_4096() -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            cvt_p(BN_get_rfc3526_prime_4096(ptr::null_mut())).map(BigNum)
        }
    }

    /// Returns a constant used in IKE as defined in [`RFC 3526`].  The prime is in the order
    /// of magnitude of `2 ^ 6144`.  This number is used during calculated key
    /// exchanges such as Diffie-Hellman.  This number is labeled MODP group 17.
    ///
    /// [`RFC 3526`]: https://tools.ietf.org/html/rfc3526#page-6
    #[corresponds(BN_get_rfc3526_prime_6114)]
    #[cfg(not(boringssl))]
    pub fn get_rfc3526_prime_6144() -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            cvt_p(BN_get_rfc3526_prime_6144(ptr::null_mut())).map(BigNum)
        }
    }

    /// Returns a constant used in IKE as defined in [`RFC 3526`].  The prime is in the order
    /// of magnitude of `2 ^ 8192`.  This number is used during calculated key
    /// exchanges such as Diffie-Hellman.  This number is labeled MODP group 18.
    ///
    /// [`RFC 3526`]: https://tools.ietf.org/html/rfc3526#page-6
    #[corresponds(BN_get_rfc3526_prime_8192)]
    #[cfg(not(boringssl))]
    pub fn get_rfc3526_prime_8192() -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            cvt_p(BN_get_rfc3526_prime_8192(ptr::null_mut())).map(BigNum)
        }
    }

    /// Creates a new `BigNum` from an unsigned, big-endian encoded number of arbitrary length.
    ///
    /// OpenSSL documentation at [`BN_bin2bn`]
    ///
    /// [`BN_bin2bn`]: https://www.openssl.org/docs/manmaster/crypto/BN_bin2bn.html
    ///
    /// ```
    /// # use openssl::bn::BigNum;
    /// let bignum = BigNum::from_slice(&[0x12, 0x00, 0x34]).unwrap();
    ///
    /// assert_eq!(bignum, BigNum::from_u32(0x120034).unwrap());
    /// ```
    #[corresponds(BN_bin2bn)]
    pub fn from_slice(n: &[u8]) -> Result<BigNum, ErrorStack> {
        unsafe {
            ffi::init();
            assert!(n.len() <= LenType::MAX as usize);

            cvt_p(ffi::BN_bin2bn(
                n.as_ptr(),
                n.len() as LenType,
                ptr::null_mut(),
            ))
            .map(|p| BigNum::from_ptr(p))
        }
    }

    /// Copies data from a slice overwriting what was in the BigNum.
    ///
    /// This function can be used to copy data from a slice to a
    /// [secure BigNum][`BigNum::new_secure`].
    ///
    /// # Examples
    ///
    /// ```
    /// # use openssl::bn::BigNum;
    /// let mut bignum = BigNum::new().unwrap();
    /// bignum.copy_from_slice(&[0x12, 0x00, 0x34]).unwrap();
    ///
    /// assert_eq!(bignum, BigNum::from_u32(0x120034).unwrap());
    /// ```
    #[corresponds(BN_bin2bn)]
    pub fn copy_from_slice(&mut self, n: &[u8]) -> Result<(), ErrorStack> {
        unsafe {
            assert!(n.len() <= LenType::MAX as usize);

            cvt_p(ffi::BN_bin2bn(n.as_ptr(), n.len() as LenType, self.0))?;
            Ok(())
        }
    }
}

impl fmt::Debug for BigNumRef {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self.to_dec_str() {
            Ok(s) => f.write_str(&s),
            Err(e) => Err(e.into()),
        }
    }
}

impl fmt::Debug for BigNum {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self.to_dec_str() {
            Ok(s) => f.write_str(&s),
            Err(e) => Err(e.into()),
        }
    }
}

impl fmt::Display for BigNumRef {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self.to_dec_str() {
            Ok(s) => f.write_str(&s),
            Err(e) => Err(e.into()),
        }
    }
}

impl fmt::Display for BigNum {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self.to_dec_str() {
            Ok(s) => f.write_str(&s),
            Err(e) => Err(e.into()),
        }
    }
}

impl PartialEq<BigNumRef> for BigNumRef {
    fn eq(&self, oth: &BigNumRef) -> bool {
        self.cmp(oth) == Ordering::Equal
    }
}

impl PartialEq<BigNum> for BigNumRef {
    fn eq(&self, oth: &BigNum) -> bool {
        self.eq(oth.deref())
    }
}

impl Eq for BigNumRef {}

impl PartialEq for BigNum {
    fn eq(&self, oth: &BigNum) -> bool {
        self.deref().eq(oth)
    }
}

impl PartialEq<BigNumRef> for BigNum {
    fn eq(&self, oth: &BigNumRef) -> bool {
        self.deref().eq(oth)
    }
}

impl Eq for BigNum {}

impl PartialOrd<BigNumRef> for BigNumRef {
    fn partial_cmp(&self, oth: &BigNumRef) -> Option<Ordering> {
        Some(self.cmp(oth))
    }
}

impl PartialOrd<BigNum> for BigNumRef {
    fn partial_cmp(&self, oth: &BigNum) -> Option<Ordering> {
        Some(self.cmp(oth.deref()))
    }
}

impl Ord for BigNumRef {
    fn cmp(&self, oth: &BigNumRef) -> Ordering {
        unsafe { ffi::BN_cmp(self.as_ptr(), oth.as_ptr()).cmp(&0) }
    }
}

impl PartialOrd for BigNum {
    fn partial_cmp(&self, oth: &BigNum) -> Option<Ordering> {
        Some(self.cmp(oth))
    }
}

impl PartialOrd<BigNumRef> for BigNum {
    fn partial_cmp(&self, oth: &BigNumRef) -> Option<Ordering> {
        self.deref().partial_cmp(oth)
    }
}

impl Ord for BigNum {
    fn cmp(&self, oth: &BigNum) -> Ordering {
        self.deref().cmp(oth.deref())
    }
}

macro_rules! delegate {
    ($t:ident, $m:ident) => {
        impl<'a, 'b> $t<&'b BigNum> for &'a BigNumRef {
            type Output = BigNum;

            fn $m(self, oth: &BigNum) -> BigNum {
                $t::$m(self, oth.deref())
            }
        }

        impl<'a, 'b> $t<&'b BigNumRef> for &'a BigNum {
            type Output = BigNum;

            fn $m(self, oth: &BigNumRef) -> BigNum {
                $t::$m(self.deref(), oth)
            }
        }

        impl<'a, 'b> $t<&'b BigNum> for &'a BigNum {
            type Output = BigNum;

            fn $m(self, oth: &BigNum) -> BigNum {
                $t::$m(self.deref(), oth.deref())
            }
        }
    };
}

impl<'a, 'b> Add<&'b BigNumRef> for &'a BigNumRef {
    type Output = BigNum;

    fn add(self, oth: &BigNumRef) -> BigNum {
        let mut r = BigNum::new().unwrap();
        r.checked_add(self, oth).unwrap();
        r
    }
}

delegate!(Add, add);

impl<'a, 'b> Sub<&'b BigNumRef> for &'a BigNumRef {
    type Output = BigNum;

    fn sub(self, oth: &BigNumRef) -> BigNum {
        let mut r = BigNum::new().unwrap();
        r.checked_sub(self, oth).unwrap();
        r
    }
}

delegate!(Sub, sub);

impl<'a, 'b> Mul<&'b BigNumRef> for &'a BigNumRef {
    type Output = BigNum;

    fn mul(self, oth: &BigNumRef) -> BigNum {
        let mut ctx = BigNumContext::new().unwrap();
        let mut r = BigNum::new().unwrap();
        r.checked_mul(self, oth, &mut ctx).unwrap();
        r
    }
}

delegate!(Mul, mul);

impl<'a, 'b> Div<&'b BigNumRef> for &'a BigNumRef {
    type Output = BigNum;

    fn div(self, oth: &'b BigNumRef) -> BigNum {
        let mut ctx = BigNumContext::new().unwrap();
        let mut r = BigNum::new().unwrap();
        r.checked_div(self, oth, &mut ctx).unwrap();
        r
    }
}

delegate!(Div, div);

impl<'a, 'b> Rem<&'b BigNumRef> for &'a BigNumRef {
    type Output = BigNum;

    fn rem(self, oth: &'b BigNumRef) -> BigNum {
        let mut ctx = BigNumContext::new().unwrap();
        let mut r = BigNum::new().unwrap();
        r.checked_rem(self, oth, &mut ctx).unwrap();
        r
    }
}

delegate!(Rem, rem);

impl<'a> Shl<i32> for &'a BigNumRef {
    type Output = BigNum;

    fn shl(self, n: i32) -> BigNum {
        let mut r = BigNum::new().unwrap();
        r.lshift(self, n).unwrap();
        r
    }
}

impl<'a> Shl<i32> for &'a BigNum {
    type Output = BigNum;

    fn shl(self, n: i32) -> BigNum {
        self.deref().shl(n)
    }
}

impl<'a> Shr<i32> for &'a BigNumRef {
    type Output = BigNum;

    fn shr(self, n: i32) -> BigNum {
        let mut r = BigNum::new().unwrap();
        r.rshift(self, n).unwrap();
        r
    }
}

impl<'a> Shr<i32> for &'a BigNum {
    type Output = BigNum;

    fn shr(self, n: i32) -> BigNum {
        self.deref().shr(n)
    }
}

impl<'a> Neg for &'a BigNumRef {
    type Output = BigNum;

    fn neg(self) -> BigNum {
        self.to_owned().unwrap().neg()
    }
}

impl<'a> Neg for &'a BigNum {
    type Output = BigNum;

    fn neg(self) -> BigNum {
        self.deref().neg()
    }
}

impl Neg for BigNum {
    type Output = BigNum;

    fn neg(mut self) -> BigNum {
        let negative = self.is_negative();
        self.set_negative(!negative);
        self
    }
}

#[cfg(test)]
mod tests {
    use crate::bn::{BigNum, BigNumContext};

    #[test]
    fn test_to_from_slice() {
        let v0 = BigNum::from_u32(10_203_004).unwrap();
        let vec = v0.to_vec();
        let v1 = BigNum::from_slice(&vec).unwrap();

        assert_eq!(v0, v1);
    }

    #[test]
    fn test_negation() {
        let a = BigNum::from_u32(909_829_283).unwrap();

        assert!(!a.is_negative());
        assert!((-a).is_negative());
    }

    #[test]
    fn test_shift() {
        let a = BigNum::from_u32(909_829_283).unwrap();

        assert_eq!(a, &(&a << 1) >> 1);
    }

    #[cfg(not(osslconf = "OPENSSL_NO_DEPRECATED_3_0"))]
    #[test]
    fn test_rand_range() {
        let range = BigNum::from_u32(909_829_283).unwrap();
        let mut result = BigNum::from_dec_str(&range.to_dec_str().unwrap()).unwrap();
        range.rand_range(&mut result).unwrap();
        assert!(result >= BigNum::from_u32(0).unwrap() && result < range);
    }

    #[cfg(not(osslconf = "OPENSSL_NO_DEPRECATED_3_0"))]
    #[test]
    fn test_pseudo_rand_range() {
        let range = BigNum::from_u32(909_829_283).unwrap();
        let mut result = BigNum::from_dec_str(&range.to_dec_str().unwrap()).unwrap();
        range.pseudo_rand_range(&mut result).unwrap();
        assert!(result >= BigNum::from_u32(0).unwrap() && result < range);
    }

    #[cfg(not(osslconf = "OPENSSL_NO_DEPRECATED_3_0"))]
    #[test]
    fn test_prime_numbers() {
        let a = BigNum::from_u32(19_029_017).unwrap();
        let mut p = BigNum::new().unwrap();
        p.generate_prime(128, true, None, Some(&a)).unwrap();

        let mut ctx = BigNumContext::new().unwrap();
        assert!(p.is_prime(100, &mut ctx).unwrap());
        assert!(p.is_prime_fasttest(100, &mut ctx, true).unwrap());
    }

    #[cfg(ossl110)]
    #[test]
    fn test_secure_bn_ctx() {
        let mut cxt = BigNumContext::new_secure().unwrap();
        let a = BigNum::from_u32(8).unwrap();
        let b = BigNum::from_u32(3).unwrap();

        let mut remainder = BigNum::new().unwrap();
        remainder.nnmod(&a, &b, &mut cxt).unwrap();

        assert!(remainder.eq(&BigNum::from_u32(2).unwrap()));
    }

    #[cfg(ossl110)]
    #[test]
    fn test_secure_bn() {
        let a = BigNum::new().unwrap();
        assert!(!a.is_secure());

        let b = BigNum::new_secure().unwrap();
        assert!(b.is_secure())
    }

    #[cfg(ossl110)]
    #[test]
    fn test_const_time_bn() {
        let a = BigNum::new().unwrap();
        assert!(!a.is_const_time());

        let mut b = BigNum::new().unwrap();
        b.set_const_time();
        assert!(b.is_const_time())
    }

    #[test]
    fn test_mod_sqrt() {
        let mut ctx = BigNumContext::new().unwrap();

        let s = BigNum::from_hex_str("2").unwrap();
        let p = BigNum::from_hex_str("7DEB1").unwrap();
        let mut sqrt = BigNum::new().unwrap();
        let mut out = BigNum::new().unwrap();

        // Square the root because OpenSSL randomly returns one of 2E42C or 4FA85
        sqrt.mod_sqrt(&s, &p, &mut ctx).unwrap();
        out.mod_sqr(&sqrt, &p, &mut ctx).unwrap();
        assert!(out == s);

        let s = BigNum::from_hex_str("3").unwrap();
        let p = BigNum::from_hex_str("5").unwrap();
        assert!(out.mod_sqrt(&s, &p, &mut ctx).is_err());
    }

    #[test]
    #[cfg(any(ossl110, boringssl, libressl350))]
    fn test_odd_even() {
        let a = BigNum::from_u32(17).unwrap();
        let b = BigNum::from_u32(18).unwrap();

        assert!(a.is_odd());
        assert!(!b.is_odd());

        assert!(!a.is_even());
        assert!(b.is_even());
    }
}